The sulfotransferases are enzymes which catalyze the sulfation of the hydroxyl functionalities of a wide variety of exogenous and endogenous compounds. The sulfation reaction involves the transfer of a sulfate group from an activated sulfate donor to an acceptor substrate to form a sulfate ester. Although enzyme catalyzed sulfation usually attenuates biological activity and facilitates excretion, it also participates in the bioactivation of several types of chemical carcinogens including safrole, aromatic hydroxylamines and hydroxamic acids, and hydroxyxanthines. ln these instances, sulfotransferase catalyzes the sulfonation of the hydroxyl group to produce very reactive, electrophilic sulfate esters. The premise of this proposal is that these reactive sulfate esters, in addition to reacting with DNA and RNA, can reactive with sulfotransferase to inactivate it in a mechanismbased manner. This possibility is supported by preliminary unpublished data which indicates that N-hydroxy-2-acetamidofluorene, a model hydroxamic acid carcinogen, irreversibly inactivates aryl sulfotransferase IV partly by a mechanism-based approach. This is the first observation of mechanism-based sulfotransferase inactivation. The proposed research involves a complete characterization of the inactivation process and experiments to clarify the scope of this phenomenon. Purified sulfotransferase isozymes will be used in these studies and the experimental approaches include kinetic experiments, the use of protective nucleophiles and specific dead-end inhibitors. Finally, mechanism- based inactivation will be investigated for its potential to provide fundamental information about the amino acid residues present at or near the enzymes active site. The information provided by the above research should improve our understanding of the complex biological effects of chemical carcinogens and an important group of metabolic enzymes.